Azeotropic distillation of propionamide



Patented Sept. 2, 1952 [UNITED STAT sznornorro ms'rmLA'rroN or Walter PROP-IONAMIDE- Eruner, Wilmington, andf Eugne Turner Darden, New Castle, Deb, assignors to ELL'duIont de Nemours & Cmpany,"W mington, DeL, a corporation oi':Dela'ware= Drawing. Applicationiiugust 25,1950, g QSerialNo. 131,556

; appear hereinafter. lnaccordance with this invention propionamide canbe separated from the said contaminating substances by adding. toithe contaminated propionamide a hydrocarbon having a boiling 'pointw-ithin the range of, 153 to 273 C preferably an alk'ane having from 10150 12 carbon atoms per molecule, and distilling from the resulting mixture an azeotrope comprising propionamide and the said hydrocarbon.

The following table gives the boiling points of certain azeotropes produced in accordance with this invention.

TABLE I Boiling points of azeotropes Boiling Points (0.") at Various Pressures Azeotrope Components 1 200 mm. 100 mm. 50 mm.

n-decane-l-propionamicle. 168 126 106 88 (11.8) (7. (5) (3) n-undecane-l-proplona- 183 142 123 105 mide. (21) (17. 3) (16) n-dodecane-I-propiona- 193 152 132 115 mide; (31.6) (26) (26) (2c) 1 The approximate propionamide content of each azeotrope is given parenthetically.

n-dodecane, giving rise to a minimum boiling azeotrope containing about 30% propionamide and 70% n-dodecane. The azeotrope boils at 3r .iaclai s. elm-42 its compounds.

115 0; "at' SO' min/ r mercury and 193 0. at 760 mm. On condensation, the az'eot'rope separates into 'two liquidphas'es, -.the lower layer beingpredominantly 1 propionamide: This lower layer is cooled," and the propionamide crystals thus obtained are'separated by filtration. This propionamide is white and free of sulfur and Example 2 .'A crudemixture containing pro- "pionade; sulfur, sulfides, disulfides, mercaptans,

unknown colored compounds-inseparable from *propionamide by ordinary; 'distillationfoils, and tars is distilled in-the presence of an excess of ndecane, giving rise to a minimumboilinghzeotrope containing about 3% propionamide, and 97% n-decane. The azeotrope boils at88fC. at

51:) mm; pressure; On condensation, the az'eotrope separates into two liquid'phasesyth e lower layer being predominantly propionamide. The distillate is cooled' 'with agitation; andpropionamide' crystals are separated by filteringthe resulting slurry.

Example 3.A crude mixture containing propionamide, sulfur, sulfides, disulfides, mercaptans, unknown colored compounds inseparable from propionamide by ordinary distillation, oils, and tars is distilled in the presence of an excess of n-undecane, giving rise to a minimum boiling azeotrope containing about 15% propionamide and n-undecane. The azeotrope boils at C.

at ,50 mm. pressure. On condensation the azeotrope separates into two liquid phases, the lower layer being predominantly propionamide. The distillate is cooled with agitation. and propionamide crystals are separated by filtering the re-' I sulting slurry. The crystals are washed free of I n-undecane by means of low boiling alkanes.

Example 4.-A hydrocarbon mixture consisting predominantly of n-undecane and n-dodecane and obtainedby distillation of Thinner, a product of Shell Oil Co., was used as an azeotropic carrier to distill white and sulfur-free propionamide from a crude mixture containing oils, tars, sulfur compounds, etc. obtained in the synthesis of propionamide from propylene and aqueous ammonium polysulfide. The propionamide contents of the azeotropes recovered were between those of n-undecane and n-dodecane when the distillation was carried out at 50 mm. pressure. However, when the distillation was carried out at 200 mm. an azeotrope containing 31.4% propionamide was obtained at about 149 C. This is more than the amount of propionamide found in the C11 or C12 azeotropes at 142 C. and 152 C. respectively.

In the foregoing examples, the propionamide layer in the azeotropic distillates contains about 1% to 3% by weight of the hydrocarbon component. This may be removed by topping the lower layer, i. e. by separating the lower layer while the distillate is hot, and redistilling it to obtain a small amount of azeotrope asforeshot, and a residue of pure propionamide. Another way by which the hydrocarbon can be removed is to cool the propionamide phase and wash it while cold with low boiling alkanes, which'removes the higher boiling hydrocarbon, as above illustrated. The low boiling alkanes can be removed from the crystals by evaporation.

It is to be understood that the foregoing examples are illustrative only and that numerous methods for practicing the invention will occur 3. The process of claim 1 in which the said 'alkane is n-undecane.

7 still and distilling therefrom a propionamideto those who are skilled in the art. For example,

the azeotropic distillation may be carried out at,

various pressures, preferably within the range of about 50 to 760 mm. Since the azeotrope contains two liquid phases, separation of the lower layer containing predominantly propionamide, followed by redistillation thereof or extraction with a solvent which is non-miscible with the hydrocarbon component are examples of suitable procedures for separating the propionamide from the azeotrope. I r

The method of the invention is of course not limited to separation of propionamide from specific reaction mixtures but may be employed wherever it is desirable to remove propionamide from other substances which are not readily separated therefrom by simple distillation or crystallization.

we claim: i p

1. In a process for purifying propionamide the step which comprises distilling propionamide azeotrcpically with normal alkane having from 10 to lzcarbon atoms per molecule.

2. The process of claim 1 in which the said alkane is n-decane. I 1

alkane azeotrope, whereby a residue of propionamide is obtained.

7. The process of claim 6 in which the said alkane is n-decane.

8. The process of claim 6 in which the said alkane is n-undecane. Y

9. The process of claim 6 in which the said alkane is a mixture of n-undecane and n-dodecane.

10. The process of claim 6 in which the said alkane is n-dodecane.

TER M. BRUNER. I RNER DARDEN.

" REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Analytical Chemistry, vol. 19, August 1947, page 541, table of azeotropic" data compiled by L'. H. Horsley. Q 

1. IN A PROCESS FOR PURIFYING PROPIONAMIDE THE STEP WHICH COMPRISES DISTILLING PROPIONAMIDE AZEOTROPICALLY WITH NORMAL ALKANE HAVING FROM 10 TO 12 CARBON ATOMS PER MOLECULE. 